1. Field of the Invention
The present invention relates to a light-emitting diode (LED) lamp, and more particularly to an LED lamp compatible with an electronic ballast generating preheating current.
2. Description of the Related Art
With reference to FIG. 2, a conventional fluorescent lamp 50 is a gas discharge lamp, which must preheat a lamp filament 52 of the fluorescent lamp 50 to ionize a gas inside the lamp.
The conventional fluorescent lamp 50 usually has a first electrode terminal L, a second electrode terminal N, a lamp tube 51, and two lamp filaments 52. The first electrode terminal L and the second electrode terminal N are respectively mounted on two ends of the fluorescent lamp 50, and are electrically connected to the AC power output terminal of an electronic ballast 60. The first electrode terminal L has two electrodes L1 and L2, and the second electrode terminal N has two electrodes N1 and N2. The two lamp filaments 52 are mounted inside the lamp tube 51, and each lamp filament 52 is mounted between the electrodes L1, L2 or between the electrodes N1, N2. When the conventional fluorescent lamp 50 is operated, if a rapid start electronic ballast or a program start electronic ballast is used, the electronic ballast will provide a preheating current to each of the first electrode terminal and the second electrode terminal. The preheating current flows through and heats the lamp filament 52 to ionize the gas inside the lamp for the fluorescent lamp 50 to emit light.
To be compatible with conventional lamp holders, most existing LED lamps follow the design of the conventional lamp tube 51. In other words, the first electrode terminal L and the second electrode terminal N on both ends of the lamp tube 51 remain unchanged. The first electrode terminal L and the second electrode terminal N are respectively connected to the LED components on both ends of a conventional LED lamp to serve as a power source. However, the conventional LED lamp has no lamp filament therein, meaning that there is no resistance (lamp filament) connected between the electrodes L1, L2 of the first electrode terminal L and between the electrodes N1, N2 of the second electrode terminal N. Hence, if the LED lamp is directly connected to a rapid start electronic ballast or a program start electronic ballast, the electronic ballast will provide a short-circuit current to the electrodes L1, L2 and the electrodes N1, N2 after the electronic ballast is powered on. Such short-circuit current can damage the electronic ballast 60 and the LED lamp and shorten the life durations of the electronic ballast 60 and the LED lamp.